Time Division Multiplexing System Research Articles

Integrated-Optic Planar Lightwave Circuits.

Planar lightwave circuits (PLCs) are waveguide devices that integrate fiber-matched optical waveguides on Silicon or glass substrate to provide an efficient means of interaction for the guided-wave optical signals. The most prominent feature of the silica waveguides is their simple and well defined waveguide structures. This allows us to fabricate multi-beam or multi-stage interference devices such as arrayed-waveguide gratings and lattice-form programmable dispersion equalizers. PLCs provide various important and functional devices for optical wavelength division multiplexing (WDM), time division multiplexing (TDM) systems and subscriber networks. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add/drop multiplexers, programmable dispersion equalizers and hybrid optoelectronics integration technologies.

Multiplexed ARQ for time-varying channels. I. System model and throughput analysis

In this paper, a model is developed for a slotted time-division multiplexing system used for assigning transmissions over a set of time-varying channels. Two schemes, a "round-robin" and an adaptive multiplexing scheme, are studied for use with three standard automatic-repeat-request (ARQ) protocols, namely, stop-and-wait (SW), go-back-N (GBN), and ideal selective repeat (ISR). In round-robin multiplexing, transmission slots are assigned periodically to each channel, With the adaptive scheme, the multiplexer selects at each time slot the channel whose state is estimated to have the lowest retransmission probability. The throughputs of these ARQ protocols under either multiplexing scheme are analyzed and compared. The present paper contains a description of the system model and an analysis of the ARQ protocols under both multiplexing schemes. In Part II, a modification to GBN and selective repeat ARQ for reducing the detrimental effects of feedback errors is discussed and analyzed, followed by a throughput performance comparison of all ARQ and multiplexing schemes.

Comparison Results for Markov-Modulated Recursive Models

We consider a general discrete-time stochastic recursive model that is influenced by an external Markov chain. Our aim is to investigate the effect that the transition matrix of the external process has on the system states of the model. To answer this question, we use new stochastic ordering concepts. Especially interesting are the results for infinite-stage Markov-modulated models. We illustrate our main results by three applications: an inventory model, a consumption model, and a queueing model for a time division multiplexing system.

Discrete time queues with phase dependent arrivals

The queueing behavior of many communication systems is well modeled by a queueing system in which time is slotted, and the number of entities that arrive during a slot is dependent upon the state of a discrete time, discrete state Markov chain. Techniques for analyzing such systems have appeared in the literature from time to time, but distributions have been presented in only rare instances In the paper, the authors present the probability generating function (PGF) for joint and marginal buffer occupancy distributions of statistical time division multiplexing systems in this class. They discuss inversion of the PGF using discrete Fourier transforms, and also discuss a simple technique for obtaining moments of the queue length distribution. Numerical results, including queue length distributions for some special cases, are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New applications of a sinusoidally driven InGaAsP electroabsorption modulator to in-line optical gates with ASE noise reduction effect

The authors propose new applications of a sinusoidally driven InGaAsP electroabsorption modulator to an inline optical gate for a 2R (reshape and retiming) repeater in optical amplifier systems, an n:1 optical demultiplexer in time division multiplexing systems, and an optical switch. The small polarization dependence of the modulator is essential for inline use. By utilizing the monotonic increase of the extinction ratio with increasing applied voltage, the electroabsorption modulator driven by a large-signal sinusoidal voltage can produce a time domain square-shaped gate function with variable gate width. Furthermore, amplified spontaneous emission noise of optical amplifier systems can be reduced in both time and wavelength domains at the off-state of the modulator, due to noninterferometric wide wavelength operation of the modulator. Experimental results for a 2R repeater, an n:1 (n=4, 8) optical demultiplexer, and optical gates for switching are also demonstrated at over 10-Gb/s repetition rate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application to a high energy physics experiment of the optical-transmission readout system

A WDM (wavelength division multiplexing) transmission system using optical fibers has been proposed for the readout system of a typical Si microstrip detector with an enormous number of channels which will be used in the near future for high-energy physics experiments at hadron or linear colliders. For example, the Si microstrip detector in the SDC (solenoidal detector collaboration) of the SSC (Superconducting Super Collider) experiment has an enormous number of readout channels (about 10 million). For a readout system with an enormous number of channels, WDM is the most effective transmission system. Further, the WDM system can enhance the transmission capability, especially by adding a TDM (time division multiplexing) system. A multiplicity of 100 was estimated for WDM, and 10 for TDM; the total multiplicity therefore amounts to 1000. >

Pulse frequency division multiplexing is a new way to increase the capacity of a local fiber-optic communications network

A method of pulse frequency division multiplexing (PFDM) to increase the capacity of a local fiber-optic communications system (hundreds of simultaneous users with a throughput of tens or potentially even hundreds of gigabits per second) is proposed. Pulse frequency (repetition rate of laser pulses or modulation rate) can, in theory, be used to identify signals from individual customers. The main advantage of the proposed technique is that the particular pulse frequency could be better controlled electrically than the particular optical frequency of semiconductor lasers. It is asynchronous, which is another advantage over time division multiplexing systems. Further development of the key components, such as optical AND gates, optical threshold devices, adjustable optical delay lines, stabilized and very short pulse laser sources, and pulse compression elements, is important for the practical realization of the proposed method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 4*5 Gb/s transmission system with all-optical clock recovery

The authors demonstrate successful 5 Gb/s operation of an all-optical clock extraction circuit in a 20 Gb/s optical time division multiplexing OTDM system. An optical clock signal was obtained by synchronizing a self-pulsating 1.56 mu m laser diode to a 5 GB/s RZ data signal, demultiplexed from a 4*5 Gb/s OTDM transmission system. Synchronization was achieved for pseudo-random-bit sequences from 2/sup 7/-1 to 2/sup 31/-1. At 2/sup 7/-1 full system bit-error-ratio (BER) measurement on one of the 5 GB/s channels using the extracted optical clock for synchronization were made with no observed penalty over transmitter clock measurements. Such clock extraction techniques may be of great importance in a wide variety of telecommunications applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ATDM with nonindependent sources

This paper presents a study of the queueing behaviour of an Asynchronous Time Division Multiplexing (ATDM) system. The mathematical model chosen to describe this system differs from prior models in that the data sources to be multiplexed may be, in some sense, correlated. More specifically, it is assumed that the number of active users of the ATDM system evolves from slot to slot according to a first order Markov chain. Under certain restrictions for the transition probabilities of this Markov chain, an explicit expression is derived for the probability generating function of the number of data packets in the ATDM-buffer. The results of the analysis are illustrated by means of an example, which shows the possibly substantial influence of the correlation among the users on the queueing behaviour of the system.

GEO modules as a natural basis for all-optical fiber logic systems

A generalized exclusive-OR (GEO) module is closely related to the physics of ultrafast, all-optical, soliton-based fiber logic gates. The authors show that a GEO module is Boolean and connectivity complete for a time-division multiplex system. Counters, time slot interchangers, AND gates, and NOR gates can be constructed from two to four GEO modules. For telecommunications, GEO modules can be used to demultiplex data, decode address headers, and provide rapid access to the network. Since GEO modules lead to minimal component implementation of some fundamental functions, they may be the natural basis for designing fiber-based logic systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Integration of wide-band service in time division multiplex systems

The authors present a TDM (time division multiplexing) channel access concept based on narrowband and wideband traffic requests which are queued in separated parallel queues. The system may be regarded as a part of a wideband integrated services digital network (ISDN). The channel access strategy follows the premise of allocating that type of customer first into service which fits best (fills out best) the nonoccupied channels. A Poisson arrival process and exponentially distributed service times for both are assumed for both traffic types, but they may have different bit rate requirements. The model involves four characteristic random variables; its joint probability is obtained by means of balance equations. Since it is difficult to determine the solution analytically, the authors develop the transition rate matrix and suggest a procedure for the numerical solution of the balance equations. Several numerical results are presented and discussed. >

Queueing analysis of an integrated services TDM system using a matrix-analytic method

A matrix-analytic method is used to analyze the queueing behavior of small time division multiplexing (TDM) integrated services systems. Such systems have priority services for time-critical traffics in which adjacent packets exhibit a strong interdependency. The TDM frame with a capacity of M packets is used to transmit the high-priority packets at every time step. Any unused capacity is utilized to transmit low-priority packets. The system can be modeled as a discrete-time system with a fluctuating number of servers for the low-priority packets. Because the number of servers is small and adjacent packets are dependent, the birth-and-death analysis is not appropriate. An algorithm, based on a modification of Neuts' method, is used to determine the boundary points required in the queuing analysis. Numerical results for two integrated services systems, each with different characteristics, are presented to demonstrate the feasibility of the analysis method and the computational algorithm. >

Time for Two: A Video TDM System That Maintains Spatial and Temporal Resolution for Two Pictures from Different Uplinks

As satellite systems grow, the space segment must be increased. Many have tried to overcome their need for additional transponders by utilizing frequency division multiplexing (FDM) of two video signals on the same transponder. This solution, although technically straightforward, reduces the downlink RF power and significantly modifies the operating parameters of the earth stations involved. Time division multiplexing (TDM), on the other hand, eliminates most of the FDM limitations, but in turn adds new requirements. TDM implies that part of the transmission time will be devoted to each of the signals to be transmitted. The question naturally arises: If less than 100% of the transmission time is provided to each picture, how are temporal or spatial losses to be avoided? The T-4–2 process recognizes the fact that in standard television transmission, each television frame is sent twice. Appropriate preand post-processing of only one frame will provide two complete frames at the receiving point. This article describes a system that also provides synchronous switching between two separated uplinks, while still maintaining spatial and temporal resolution of the picture.

Integration of Discrete-Time Correlated Markov Processes in a TDM System

In this paper, we consider a discrete-time queueing model for a Time Division Multiplexing (TDM) system with integration of voice and data (a model introduced by Li and Mark [16]). The voice traffic is a superposition of N Markov chains, which alternate between two states: the talkspurt state and the silence state. The data traffic is Poisson and independent of the voice sources. We show that the average queue size is increasing in certain correlation coefficients of the voice sources, increasing convex in the proportion of time the voice sources are in talkspurts, increasing convex in the number of voice sources, and increasing convex in the data traffic intensity. However, it is decreasing convex in the number of channels. These structural results yield various bounds. To take video traffic into account as well, we adapt a model of Maglaris et al. [18]. In their model, video traffic is generated by a continuous-state autoregressive Markov process that matches the average rate and the autocovariance of the output of a video coder. We show that if we replace their autoregressive model by a two-state Markov chain model with the same rate and correlation coefficient, we obtain an upper bound for the queue size. This replacement enables us to treat the video traffic as a voice source and use the techniques developed for dealing with voice/data integration to obtain bounds and estimates.

Traffic characterization for integrated services networks

A discrete-time queuing analysis is presented for integration of multiple traffic types in a packet-switched TDM (time-division multiplexing) system. The correlation of each traffic type is represented in terms of the power spectral density. The general expression obtained for the aggregate mean queue size indicates that slowly varying traffic types exert the largest effect on the queuing process. Also, a lengthy-steady traffic is highly predictable. An adaptive flow control and routing scheme, based on signal prediction, which successively adjusts the short-burst traffic arrival rate at each TDM node, is introduced and analyzed. The analytical results indicate a substantial reduction in the correlation effect on the system queuing behavior. >

A Channel Access Protocol for Integrated Voice/Data Applications

A new multiaccess protocol is proposed for an integrated voice/data application. The protocol, which is a variation of virtual time CSMA (VT-CSMA), takes advantage of the periodicity of voice packets and possesses a number of important features. With this protocol, voice stations appear to have a dedicated time-division multiplexed (TDM) slot, and the delay of a voice packet is bounded by the length of a frame (defined to be the period between two consecutive voice packets from a voice station). Also, the amount of data added to the channel has little effect on the voice traffic. When silence detection is used, many more voice conversations can be supported without losing the dedicated-slot characteristic. This is in contrast to a movingboundary TDM system where the excessive bandwidth saved by silence detection can only be used for data. The protocol requires no global synchronization and is easy to implement. Simulation results are presented to evaluate its performance.

Six-channel time-division multiplexed system for recording analogue data on the audio track of a videotape.

A time-division multiplexer system employing a modified form of pulsewidth modulation to record six low-frequency analogue data on a single audio track of a videotape recorder is described. For each channel the data sampling rate is 200 per second, allowing an input data bandwidth of DC to 40 Hz. To obtain maximum signal-to-noise ratio with acceptably low adjacent-channel crosstalk, the recorded signal comprises narrow positive and negative pulses that correspond to the leading and trailing edges, respectively, of the width-modulated pulses. A demultiplexer/demodulator restores the original six low-frequency analogue signals by developing the train of width-modulated pulses from the signal replayed from tape, separating them and passing them to individual demodulators. For each output channel, frequency response is 0–40 Hz, overall linearity is within±1 per cent and peak-to-peak noise and adjacent-channel crosstalk amount to less than 1 per cent of maximum peak-to-peak output. Tape speed fluctuations have little effect on baseline but cause small variations in demodulator sensitivity. These effects of tape speed fluctuations can be eliminated completely using an alternative demodulator that requires output bandwidth to be limited to 0–25 Hz.

Microprocessor-based synchronization unit for a delta-modulated TDM system

Abstract This paper describes design and implementation aspects of a microprocessor-based synchronization unit for a delta-modulated time division multiplexing (DM-TDM) system. In its prototype design we used an Intel 8088 microprocessor and the system was assumed to consist of only eight multiplexed channels. Seven of these channels are used for data transfer and one channel is used for synchronization of transmitter (TRX) and receiver (RCX). In order to achieve synchronization between TRX and RCX, a continuous stream of a synchronization (SYNCH) word is sent on the synchronization channel. In such a system there is some loss of data during the synchronization process. However, as the DM-TDM system is primarily used for speech communication, the loss is negligible. This is because it takes only a few milliseconds, at the most, to synchronize the system.

A technique for voice multiplexing

In a, multiplexing system the mutual interference between users is limited, by the use of either orthogonal functions such as in frequency division multiplexing (FD.M) and time division multiplexing (TDM) systems or ‘ almost orthogonal ’ codes such as in spread spectrum multiplexing (SSM) systems. The badnwidth required for the second ease is much wider than the one for the first case considering the same signal to noise ratio (SNR). In this paper, a technique relevant to SSM is described, in which specially constructed encoding sequences replace the ‘ almost orthogonal’ codes exclusively used in SSM systems. This results in a significant reduction in the bandwidth requirements for the same SNR. The corresponding multiplexing system has successfully been applied to the transmission of four voice channels via transceivers with X-mode facilities (16 kHz bandwidth), which normally can handle only one digital voice channel. The system is easier to work with these transceivers than other multiplexing systems (...

Transmission of Two NTSC Color Television Signals Over a Single Satellite Transponder Via Time-Frequency Multiplexing

We describe a time-frequency multiplexing (TFM) method for transmitting two television signals over one satellite transponder, which gives significant improvement over existing methods. The complexity of the hardware implementation is similar to existing time-division multiplexing (TDM) systems, but the picture quality, when received on a 10 m earth station, approaches that which is currently being requested by the major television networks. Unlike existing frequency-division multiplexing (FDM) systems, TFM needs no backoff of the satellite transponder. The general philosophy of TFM is described, including the benefits of using a difference signal to reduce the overall required bandwidth. Also discussed is companding of the difference signal as a means of improving the overall signal-to-noise ratio. Several alternative methods of implementation are considered, along with those which have been explored in some detail. We then describe an experimental TFM system which was implemented using digital field memories and tested with a 10 m earth station operating through the COMSTAR D2 satellite. Received picture quality was excellent in all cases. Weighted SNR was 53-56 dB, and in practically all instances subjects could not tell any difference between single-picture FM transmission and TFM dual-picture transmission.